1. Field of the Invention
The present invention relates to a fuel cutoff valve that is attached to a top end of a fuel tank and functions to connect and disconnect the fuel tank with and from outside according to the liquid level in the fuel tank.
2. Description of the Related Art
A known fuel cutoff valve is disclosed, for example, in JP No. 6-297968A. This prior art fuel cutoff valve has a casing with a connection conduit connected to outside of a fuel tank, a cylindrical first float valve arranged in a valve chamber in the casing, a second float valve arranged in a vertically movable manner in a storage chamber of the first float valve, and a spring supporting these elements. The first float valve closes the connection conduit when a liquid level in the fuel tank exceeds a preset first liquid level. The second float valve closes the connection conduit when the liquid level in the fuel tank exceeds a preset second liquid level. This prevents leakage of fuel from the fuel tank to a canister during a fuel supply or in a vehicle rocking attitude.
In this prior art fuel cutoff valve, the spring functions to move up and down the first float valve and the second float valve, which are composed of a material having a greater specific gravity than that of the fuel. The movement of the float valve can thus not follow the rise speed of the liquid level in the fuel tank. Namely the prior art fuel cutoff valve can not quickly close to prevent leakage of the fuel from the fuel tank under a large transverse force or under a large upthrust force, which may arise during a turn of the vehicle.